1. Field of the Invention
The present invention relates to an actuator that enables a slider to effect reciprocating motion linearly along a frame under the driving action of a driving source.
2. Description of the Related Art
A transport means such as an actuator has been hitherto used, for example, in order to transport a workpiece. Japanese Laid-Open Patent Publication No. 2003-74551 discloses an actuator implementing this conventional technique.
As shown in FIG. 14, the actuator comprises an inner block 2 that is displaceable in the axial direction within an outer rail 1. A ball screw shaft 3 is provided at a substantially central portion of the inner block 2 so that the ball screw shaft 3 extends in the axial direction.
A pair of first ball-rolling grooves 4 is formed in the axial direction along a pair of inner wall surfaces 1a, 1b of the outer rail 1 opposed to the inner block 2. Further, second ball-rolling grooves are formed on both side surfaces of the inner block 2 opposed to the first ball-rolling grooves 4 in the same manner as described above. Return passages 7, in which a plurality of balls 6 is circulated, are formed in the inner block 2. The balls 6 are circulated through the return passages 7, the first ball-rolling grooves 4, and the second ball-rolling grooves 2, and thus the inner block 2 is guided as it is displaced along the outer rail 1.
The ball screw shaft 3, which is integrally connected to a driving source such as an unillustrated electric motor, is rotated, whereby the inner block 2, which is screw-engaged with the ball screw shaft 3, is displaced linearly in the axial direction of the outer rail 1 under the rotary action of the ball screw shaft 3.
However, the actuator disclosed in Japanese Laid-Open Patent Publication No. 2003-74551 requires a plurality of balls 6, which roll along endless circulating tracks as the guide mechanism for guiding the inner block 2 in the axial direction of the outer rail 1. Further, it is necessary to perform highly accurate processing operations, for example, for forming the first ball-rolling grooves 4, the second ball-rolling grooves, and the return passages 7, in order to allow the balls 6 to roll smoothly therein. Therefore production costs for the actuator are expensive.